feathers_gallery infinite update loop fix (#23827)

# Objective

In the `feathers_gallery` example, on a `TextEditChange`
`handle_hex_color_change` updates `DemoWidgetStates` which causes
`update_colors` to update the hex input triggering another
`TextEditChange`.

## Solution

Only update `DemoWidgetStates` in `handle_hex_color_change` if the new
color is different.

Author: ickshonpe

examples/ui/widgets/feathers_gallery.rs

@@ -713,7 +713,9 @@ fn handle_hex_color_change(
     mut colors: ResMut<DemoWidgetStates>,
 ) {
     let editable_text = *q_text_input;
-    if let Ok(color) = Srgba::hex(editable_text.value().to_string()) {
+    if let Ok(color) = Srgba::hex(editable_text.value().to_string())
+        && color != colors.rgb_color
+    {
         colors.rgb_color = color;
     }
 }